Flat heat pipe and method for manufacturing the same

ABSTRACT

An exemplary flat heat pipe with an evaporator section and a condenser section at opposite ends thereof includes a hollow flat casing, a first wick structure and a solid and sintered second wick structure. The first wick structure includes a top plate and a bottom plate opposite to the top plate. The first wick structure is received in the casing, and extends from the evaporator section to the condenser section. The second wick structure is disposed in the casing at the evaporator section. The second wick structure contacts the top and bottom plates and joins the first wick structure. A method for manufacturing the heat pipe is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to two co-pending applications respectively entitled “FLAT HEAT PIPE WITH VAPOR CHANNEL” (attorney docket number US32037) and “FLAT HEAT PIPE” (attorney docket number US32038), assigned to the same assignee of this application and filed on the same date as this application. The two related applications are incorporated herein by reference.

BACKGROUND

1. Technical Field

The disclosure generally relates to a heat transfer apparatus, and particularly to a flat heat pipe with high heat transfer efficiency.

2. Description of Related Art

Heat pipes are widely used in various fields for heat dissipation purposes due to their excellent heat transfer performance. One commonly used heat pipe includes a sealed tube made of thermally conductive material with a working fluid contained therein. The working fluid conveys heat from one end of the tube, typically referred to as an evaporator section, to the other end of the tube, typically referred to as a condenser section. Preferably, a wick structure is provided inside the heat pipe, lining an inner wall of the tube, and drawing the working fluid back to the evaporator section after it condenses at the condenser section.

During operation, the evaporator section of the heat pipe maintains thermal contact with a heat-generating electronic component. The working fluid at the evaporator section absorbs heat generated by the electronic component, and thereby turns to vapor. Due to the difference in vapor pressure between the two sections of the heat pipe, the generated vapor moves, carrying the heat with it, toward the condenser section. At the condenser section, the vapor condenses after transferring the heat to, for example, fins thermally contacting the condenser section. The fins then release the heat into the ambient environment. Due to the difference in capillary pressure which develops in the wick structure between the two sections, the condensate is then drawn back by the wick structure to the evaporator section where it is again available for evaporation.

In ordinary use, the heat pipe is flattened to increase a contact area with the electronic component and enable smaller electronic products to incorporate the heat pipe. However, this may result in damage to the wick structure of the heat pipe. When the wick structure of the heat pipe is damaged, the flow resistance of the wick structure is liable to be considerably increased. In such case, the condensate may not be retrieved from the condenser section in a timely manner, and the heat pipe eventually dries out at the evaporator section.

What is needed, therefore, is a flat heat pipe and a method for manufacturing the heat pipe which can overcome the described limitations.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead placed upon clearly illustrating the principles of the present embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the various views, and all the views are schematic.

FIG. 1 is an abbreviated, side plan view of a heat pipe in accordance with a first embodiment of the disclosure.

FIG. 2 is an enlarged, transverse cross section of the heat pipe of FIG. 1, taken along line II-II thereof.

FIG. 3 is an enlarged, transverse cross section of the heat pipe of FIG. 1, taken along line thereof.

FIG. 4 is similar to FIG. 2, but shows a transverse cross section of a heat pipe according to a second embodiment of the disclosure.

FIG. 5 is similar to FIG. 2, but shows a transverse cross section of a heat pipe according to a third embodiment of the disclosure.

FIG. 6 is a flowchart showing an exemplary method for manufacturing the heat pipe of FIG. 1.

FIG. 7 is an exploded, isometric view of a cylindrical tube and a cylindrical mandrel used for manufacturing the heat pipe according to the method of FIG. 6.

FIG. 8 is a transverse cross section of a semi-finished heat pipe manufactured according to the method of FIG. 6, showing two first wick structures and a second wick structure received in the cylindrical tube of FIG. 7.

DETAILED DESCRIPTION

Referring to FIGS. 1-3, a heat pipe 10 in accordance with a first embodiment of the disclosure is shown. The heat pipe 10 is a flat heat pipe, and includes a flat tube-like casing 11 with two ends thereof sealed, and a variety of elements enclosed in the casing 11. Such elements include two first wick structures 12, 13, a second wick structure 14, and a working medium (not shown).

The casing 11 is made of metal or metal alloy with a high heat conductivity coefficient, such as copper, copper-alloy, or other suitable material. The casing 11 is elongated, and has an evaporator section 111 and an opposite condenser section 113 along a longitudinal direction thereof. The casing 11 has a width larger than its height. In particular, the casing 11 has a flattened transverse cross section. To meet the weight requirements of common electronic products, the height of the casing 11 is preferably less than 2 millimeters (mm) The casing 11 is hollow, and includes a top plate 114, a bottom plate 115 opposite to the top plate 114, and two side plates 116, 117 interconnecting the top and bottom plates 114, 115. The top and bottom plates 114, 115 are flat and parallel to each other. The side plates 116, 117 are arcuate and respectively disposed at opposite lateral sides of the casing 11.

The first wick structures 12, 13 are elongated hollow tubes, and extend longitudinally from the evaporator section 111 to the condenser section 113. An inner space 140 is longitudinally defined in each of the first wick structures 12, 13. The first wick structures 12, 13 are monolayer-type structures, formed by weaving a plurality of metal wires such as copper or stainless steel wires. The first wick structures 12, 13 thus have a plurality of pores therethrough. Alternatively, the first wick structures 12, 13 can be multilayer-type structures layered along a radial direction thereof by weaving a plurality of metal wires. Each first wick structure 12, 13 has a flattened transverse cross section, similar in principle to the flattened transverse cross section of the casing 11. In particular, each first wick structure 12, 13 includes a top wall 121, a bottom wall 122 opposite to the top wall 121, and two sidewalls 123, 124 interconnecting the top and bottom walls 121, 122. The top and bottom walls 121, 122 are flat and parallel to each other. The top and bottom walls 121, 122 contact the top and bottom plates 114, 115 of the casing 11, respectively. The sidewalls 123, 124 are arcuate and respectively disposed at opposite lateral sides of each first wick structure 12, 13.

The first wick structures 12, 13 are spaced from each other, and also from the side plates 116, 117 of the casing 11. The sidewall 123 of the first wick structure 12 and the side plate 116 adjacent to the first wick structure 12 cooperatively define a first vapor channel 141 therebetween. The sidewall 123 of the first wick structure 13 and the side plate 117 adjacent to the first wick structure 13 cooperatively define a second vapor channel 142 therebetween. The two first wick structures 12, 13 cooperatively define a third vapor channel 143 therebetween. The third vapor channel 143 is located at a center of the casing 11. The first, second and third vapor channels 141, 142, 143, provide passages through which the vapor flows from the evaporator section 111 to the condenser section 113.

The second wick structure 14 is disposed along a center axis of the evaporator section 111, and contacts the top and bottom plates 114, 115 of the casing 11. The second wick structure 14 occupies a portion of the third vapor channel 143 at the evaporator section 111 of the casing 11. The second wick structure 14 is a solid wick structure made of sintered copper powder. The second wick structure 14 is joined to the sidewalls 124 of the first wick structures 12, 13 via sintering. The first and second wick structures 12, 13, 14 cooperatively form a composite wick structure 17 in the casing 11. The first and second channels 141, 142 are defined between opposite lateral sides of the composite wick structure 17 and the side plates 116, 117 of the casing 11, respectively.

The working medium is saturated in the first and second wick structures 12, 13, 14. The working medium is usually selected from a liquid such as water, methanol, or alcohol, which has a low boiling point. The casing 11 of the heat pipe 10 is evacuated and hermetically sealed after the working medium is injected into the casing 11 and saturated in the first and second wick structures 12, 13, 14. Thus, the working medium can easily evaporate when it receives heat at the evaporator section 111 of the heat pipe 10.

In operation, the evaporator section 111 of the heat pipe 10 is placed in thermal contact with a heat source (not shown) that needs to be cooled. The heat source can, for example, be a central processing unit (CPU) of a computer. The working medium contained in the evaporator section 111 of the heat pipe 10 is vaporized when receiving heat generated by the heat source. The generated vapor moves from the evaporator section 111 via the vapor channels 141, 142 to the condenser section 113. After the vapor releases its heat and condenses in the condenser section 113, the condensate is returned by the first and second wick structures 12, 13, 14 to the evaporator section 111 of the heat pipe 10, where the condensate is again available for evaporation.

In the present heat pipe 10, the second wick structure 14 is solid, and contacts the top and bottom plates 114, 115 of the casing 11. Therefore, the second wick structure 14 provides support for the casing 11 during flattening of the heat pipe 10. This prevents blockage of the vapor channels 141, 142, 143, promoting vapor flow through the heat pipe 10. In addition, the first wick structures 12, 13 are not easily damaged during the flattening. Furthermore, the first and second wick structures 12, 13, 14 cooperatively form the composite wick structure 17 at the evaporator section 111 of the heat pipe 10. This increases capillary force, and reduces flow resistance and heat resistance. As a result, the condensate is returned to the evaporator section 111 of the heat pipe 10 rapidly, thus preventing potential drying out at the evaporator section 111. Moreover, the second wick structure 14 is not disposed in the condenser section 113 of the heat pipe 10. This enlarges the vapor channels in the condenser section 113, and further promotes the flow of the working medium in the heat pipe 10.

In alternative embodiments, the quantity of first and second wick structures in the heat pipe 10 can vary. The following embodiments include examples of such variations.

Referring to FIG. 4, a heat pipe 20 in accordance with a second embodiment of the disclosure is shown. The heat pipe 20 has the same structure as the heat pipe 10 of the first embodiment, except for the wick structures. In the heat pipe 20, there is only one first wick structure 22. The first wick structure 22 is disposed in the center of the casing 11. A second wick structure 24 has a generally rectangular cross section, with the first wick structure 22 being embedded in the second wick structure 24. The first and second wick structures 22, 24 cooperatively form a composite wick structure 27 in an evaporator section 211 of the heat pipe 20. In the evaporator section 211 of the heat pipe 20, opposite lateral sides of the second wick structure 24 and the side plates 116, 117 of the casing 11 cooperatively define a first vapor channel 241 and a second vapor channel 242 therebetween, respectively. In other words, the first and second channels 241, 242 are defined between opposite lateral sides of the composite wick structure 27 and the side plates 116, 117 of the casing 11, respectively.

Referring to FIG. 5, a heat pipe 30 in accordance with a third embodiment of the disclosure is shown. The heat pipe 30 has the same structure as the heat pipe 10 of the first embodiment, except for the wick structures. In the heat pipe 30, there are three first wick structures 12, 13, 35. The first wick structure 35 is disposed in the center of the casing 11, and is embedded in a second wick structure 34.

FIG. 6 summarizes an exemplary method for manufacturing the heat pipe 10. The method includes the following steps:

Referring also to FIGS. 7 and 8, firstly, a mandrel 15, two first wick structures 16, 17, and a tube 18 are provided. The mandrel 15 is elongated and generally cylindrical, and defines two longitudinal slots 152, 153 in a circumferential surface 151 thereof. The slots 152, 153 are symmetrical relative to each other, and span through both a front end surface and a rear end surface of the mandrel 15. A cross section of each of the slots 152, 153 defines part of a circle, i.e., a large sector. A front end of the mandrel 15 further defines a cutout 154 in a portion of the circumferential surface 151 between the slots 152, 153. The cutout 154 is axially shorter than each slot 152, 153. The cutout 154 defines a generally rainbow-shaped cross section, and communicates with the slots 152, 153. The tube 18 is hollow and cylindrical, and is made of highly heat conductive metal, such as copper, and so on. An inner diameter of the tube 18 is substantially equal to an outer diameter of the mandrel 15. The first wick structures 16, 17 are hollow and cylindrical, and each have an annular cross section. Each of the first wick structures 16, 17 has an outer diameter substantially equal to an inner diameter of Page of each of the slots 152, 153 of the mandrel 15.

The first wick structures 16, 17 are horizontally inserted into the slots 152, 153 of the mandrel 15, respectively. The mandrel 15 with the first wick structures 12, 13 is inserted into the tube 18. An amount of metal powder is filled into the cutout 154 of the mandrel 15 in the tube 18. The tube 18 with the mandrel 15, the metal powder and the first wick structures 16, 17 is heated at high temperature until the metal powder sinters to form a second wick structure 19. The second wick structure 19 is thereby attached to an inner surface of the tube 18, and joins the first wick structures 16, 17. The mandrel 18 is then drawn out of the tube 18. Subsequent processes such as injecting a working medium into the tube 18, and evacuating and sealing the tube 18, can be performed using conventional methods. Thereby, a straight circular heat pipe 40 is attained. Finally, the circular heat pipe 40 is flattened until the second wick structure 19 contacts the flattened tube 18 at opposite sides thereof, thus forming the flat heat pipe 10 as illustrated in FIGS. 1-3. That is, the flattened tube 18 forms the casing 11, the flattened first wick structures 16, 17 form the first wick structures 12, 13, and the flattened second wick structure 19 forms the second wick structure 14.

Advantages of the method include the following. The cutout 154 is defined in a portion of the circumferential surface of the front end of the mandrel 15. As a result, the second wick structure 19 is attached to a portion of the inner surface of the tube 18 between the two first wick structures 16, 17. Thus, the second wick structure 19 is not easily damaged during the flattening operation.

It should be understood that the cutout 154 and the slots 152, 153 of the mandrel 15 are adapted for forming the first and second wick structures 12, 13, 14. The configurations and arrangements of the cutout 154 and the slots 152, 153 can be changed according to the particular wick structures needed to for another kind of desired flat heat pipe.

It is to be further understood that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

1. A flat heat pipe with an evaporator section and a condenser section at opposite ends thereof, the flat heat pipe comprising: a hollow flat casing comprising a top plate and a bottom plate opposite to the top plate; a first wick structure received in the casing and extending from the evaporator section to the condenser section; and a solid, sintered second wick structure disposed in the casing at the evaporator section, the second wick structure contacting the top and bottom plates and joining the first wick structure.
 2. The flat heat pipe of claim 1, wherein the second wick structure is disposed along a center axis of the evaporator section.
 3. The flat heat pipe of claim 1, wherein the first wick structure is a hollow tube made of woven wires.
 4. The flat heat pipe of claim 1, wherein the first and second wick structures cooperatively form a composite wick structure via sintering.
 5. The flat heat pipe of claim 4, wherein a vapor channel is defined between the composite wick structure and a lateral inner surface of the casing.
 6. The flat heat pipe of claim 1, further comprising another first wick structure, the second wick structure disposed between the two first wick structures.
 7. The flat heat pipe of claim 6, wherein the casing further comprises two side plates interconnecting the top and bottom plates, one of the two first wick structures and one of the two side plates cooperatively define a first vapor channel therebetween, and the other first wick structure and the other side plate cooperatively define a second vapor channel therebetween.
 8. The flat heat pipe of claim 1, wherein the first wick structure is enclosed in the second wick structure at the evaporator section.
 9. The flat heat pipe of claim 8, wherein the casing further comprises two side plates interconnecting the top and bottom plates, one of two lateral sides of the second wick structure and one of the two side plates cooperatively define a first vapor channel therebetween, and the other lateral side of the second wick structure and the other side plate cooperatively define a second vapor channel therebetween.
 10. The flat heat pipe of claim 1, further comprising another two first wick structures, wherein two of the three first wick structures are disposed at opposite sides of the second wick structure, respectively, and the other first wick structure is enclosed in the second wick structure at the evaporator section.
 11. The flat heat pipe of claim 10, wherein the casing further comprises two side plates interconnecting the top and bottom plates, one of the two first wick structures disposed at opposite sides of the second wick structure and one of the two side plates cooperatively define a first vapor channel therebetween, and the other of the two first wick structures disposed at opposite sides of the second wick structure and the other side plate cooperatively define a second vapor channel therebetween.
 12. A flat heat pipe with an evaporator section and a condenser section at opposite ends thereof, the flat heat pipe comprising: a hollow flat casing cooperatively formed by a top plate, a bottom plate opposite to the top plate, and two side plates interconnecting the top and bottom plates; and a composite wick structure disposed in the casing, the composite wick structure comprising a first wick structure in the form of woven wires, and a solid, sintered second wick structure joining the first wick structure, the first wick structure extending from the evaporator section to the condenser section, the second wick structure disposed only in the evaporator section, and the first and second wick structures contacting the top and bottom plates of the casing.
 13. The flat heat pipe of claim 12, wherein the second wick structure is disposed along a center axis of the evaporator section.
 14. The flat heat pipe of claim 12, wherein a first vapor channel and a second vapor channel are respectively defined between two lateral sides of the structure and the two side plates of the casing.
 15. The flat heat pipe of claim 14, wherein the first wick structure is enclosed in the second wick structure in the evaporator section, and the first and second vapor channels are respectively defined between two lateral sides of the second wick structure and the two side plates of the casing.
 16. The flat heat pipe of claim 14, wherein the composite wick structure further comprises another one first wick structure, the second wick structure is disposed between the two first wick structures, and the first and second vapor channels are respectively defined between the two first wick structures and the two side plates of the casing.
 17. The flat heat pipe of claim 16, wherein the composite wick structure further comprises another one first wick structure enclosed in the second wick structure in the evaporator section.
 18. A method for manufacturing a heat pipe, the method comprising: providing a cylindrical mandrel, a hollow cylindrical tube and a first wick structure, the mandrel defining a longitudinal slot in a circumferential surface thereof, one end of the mandrel defining a cutout in the circumferential surface, the cutout communicating with the slot, and an inner diameter of the tube being substantially equal to an outer diameter of the mandrel; inserting the mandrel and the first wick structure into the tube, the first wick structure received in the slot of the mandrel; filling an amount of metal powder into the cutout of the mandrel in the tube, and sintering the metal powder to form a solid second wick structure, wherein the second wick structure is joined to the first wick structure and part of an inner surface of the tube; drawing the mandrel out of the tube; injecting a working medium into the tube, and evacuating and sealing the tube; and flattening the tube until the second wick structure contacts another part of the inner surface of the tube, the two parts of the inner surface of the tube being at opposite sides of the flattened tube.
 19. The method for manufacturing a heat pipe of claim 18, wherein the cutout is axially shorter than the slot.
 20. The method for manufacturing a heat pipe of claim 19, wherein the cutout defines a generally rainbow-shaped cross section. 